Allowed and forbidden hyperfine structure of Mn2+ ions in sodium tetraborate glasses-an EPR and optical study

Murali, A and Chakradhar, Sreekanth RP and Rao, Lakshmana J (2005) Allowed and forbidden hyperfine structure of Mn2+ ions in sodium tetraborate glasses-an EPR and optical study. In: Physica B: Condensed Matter, 358 (1-4). pp. 19-26.

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Abstract

Glass systems of composition (100_x) $Na_2B_4O_7 . H_2O+xMnSO_4 . H_2O$ (x = 0, 0.1, 0.3, 0.5, 0.75, 1, 1.25, 1.5, 1.75 and 2 mol%) have been studied by using electron paramagnetic resonance (EPR) and optical absorption techniques. The room temperature EPR spectra exhibit resonance signals at g \approx 2:0 with a sextet hyper.ne structure (hfs) besides two weak signals at g \approx 3:3 and 4.3. The resonance signal at g \cong 2:0 is due to Mn2+ ions in an environmentclose to octahedral symmetry, whereas the resonances at g \cong 3:3 and 4.3 are attributed to the rhombic surroundings of the Mn2+ ions. Itis observed that for x = 1:25mol% in sodium tetra borate glasses (NTB) the EPR spectrum exhibits a good resolution of allowed as well as forbidden hfs at g \approx 2:0: The Mn2+ ions in NTB glasses (with A \approx 95 G) are quite ionic in nature. The number of spins (N) participating in resonance at g \approx 2:0 has been calculated by comparing the area under the absorption curve with that of a standard of known concentration. A linear relationship is observed between log N and 1/T in accordance with the Boltzmann law. Magnetic susceptibilities (\chi) were calculated from the EPR spectra at different temperatures. The susceptibility is varying inversely with temperature in accordance with the Curie law, and the Curie constant is evaluated from the 1/ \chi versus T graph. The zero-.eld splitting parameter D has also been calculated from the allowed hyper.ne (HF) lines. The D value was found to be dependent on temperature. The optical absorption spectrum exhibits a single broad band centered around 470nm and was assigned to the $^6A_l_g(S) \rightarrow ^4T_l_g(G)$ transition. From the ultra violet absorption edges the optical bandgap and Urbach energies have been evaluated.

Item Type: Journal Article Copyright for this article belongs to Elsevier Science. Hyperfine structure;Mn2+ ions;Na2B4O7 glasses;EPR;Optical absorption Division of Physical & Mathematical Sciences > Physics 27 May 2005 19 Sep 2010 04:18 http://eprints.iisc.ernet.in/id/eprint/2868